Lymphangiomyomatosis (LAM) is a lung disease affecting women with a distinctive histologic pattern of diffuse smooth muscle proliferation and cystic degeneration of the lung interstitium. LAM can occur in the absence of systemic disease ("sporadic LAM") or in women with tuberous sclerosis ("TSC-associated LAM"). Tuberous sclerosis (TSC) is an autosomal dominant syndrome characterized by seizures, mental retardation, and tumors of the brain, kidney, heart, and skin. LAM affects about 5 percent of women with TSC. TSC is associated with mutations in two genes: TSC1, on chromosome 9q34, and TSC2, on chromosome 16p13. TSC1 and TSC2 appear to be tumor suppressor genes. TSC1 or TSC2 loss of heterozygosity has been demonstrated in several types of TSC tumors, including renal angiomyolipomas. One objective of this proposal is to investigate the genetic mechanisms leading to smooth muscle proliferation in LAM. We have found absence of tuberin immunoreactivity in some cases of both TSC-associated and sporadic LAM. This is consistent with the "two hit" tumor suppressor gene model. To understand whether LAM fits this model, we will analyze LAM cells for clonality and loss of heterozygosity. We will also determine whether a relationship exists between specific types of TSC1 or TSC2 mutations and the development of LAM. A genotype-phenotype correlation might explain the fact that only 5 percent of women with TSC get LAM. Another objective of this proposal is to determine the relationship between sporadic LAM and TSC. Renal angiomyolipomas, which are benign tumors consisting of fat, smooth muscle, and dysmorphic vessels, occur in 70 percent of patients with TSC and in 40 percent of women with sporadic LAM. We found chromosome 16p13 (TSC2) loss of heterozygosity in renal angiomyolipomas from 7 women with sporadic LAM. This suggests that some women with sporadic LAM have underlying TSC2 gene mutations. These mutations could be either germline or somatic. We anticipate that this project will elucidate the genetic mechanisms leading to LAM. The long-term goals of this work are to understand the roles of TSC1 and TSC2 in cellular pathways controlling normal smooth muscle growth and differentiation, and to determine how disruptions in these pathways lead to disease. This work may lead to new diagnostic and therapeutic strategies for women with LAM, and may also have relevance to other diseases involving smooth muscle growth, including pulmonary fibrosis.